In recent years, wireless cellular systems typified by cellular telephone systems and the like have diversified their service patterns, and have been demanded to transmit large-capacity data such as static images, moving pictures and the like as well as speech data. To meet such demands, it has been studied actively to transmit large-capacity data using a high-frequency radio band.
In using high-frequency radio band, the degree of attenuation due to the transmission distance becomes a problem. In other words, high transmission rates are obtained at locations near the transmitting station, but only low transmission rates are achieved at locations a predetermined distance or more apart from the transmitting station. Accordingly, to consider the actual operations of the communication system, it is necessary to cover a service area by installing a large number of base stations. However, installation of a large number of base stations requires significant cost. From such circumstances, a technique is strongly demanded that implements large-capacity communication service without increasing the number of base stations to install.
There is multi-hop communication, as one of methods for expanding the service area of a base station. This technique is a communication technique where a relay station installed in the base station service area relays and transmits a signal of a mobile station out of the service area to the base station (for example, see Non-Patent Document 1).
Multi-hop communication is broadly divided into regenerative relay and non-regenerative relay. In regenerative relay, a relay station once demodulates and decodes a received signal, encodes and modulates the signal again using a modulation scheme and coding rate (Modulation and Coding Scheme: MCS) in accordance with channel quality, and then transmits the result. In contrast, in non-regenerative relay, the relay station amplifies a received signal and transmits the signal without change. In comparison with non-regenerative relay, regenerative relay provides an advantage of enabling a relay using an adequate MCS in accordance with channel quality, yet also has a disadvantage of increasing the delay due to relay. Meanwhile, non-regenerative relay provides an advantage of decreasing the delay due to relay yet also has a disadvantage of making the SNR degrade by amplifying noise. Non-patent Document 1: Hasegawa et al. “Multi-hop System for Adaptive Modulation using Regenerating Fixed Hop Stations” Technical Report of IEICE, October 2004, A/P 2004-189, RCS2004-210, pp. 57-61.